Photolysis of acetophenone derivatives with [alpha]-cyclopropyl substituents

• Published in: Journal of physical organic chemistry Vol. 28; no. 2; p. 137
• Main Authors: Ranaweera, Ranaweera A A Upul, Weragoda, Geethika K, Bain, John, Watanabe, Shinji, Abe, Manabu, Gudmundsdottir, Anna D
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 01.02.2015
• Subjects: Lasers
• ISSN: 0894-3230; 1099-1395
• DOI: 10.1002/poc.3389

Laser flash photolysis of cyclopropyl(phenyl)methanone 6 in argon-saturated methanol yields the triplet ketone (T1K) of 6 that is formed with a rate constant of ~1.7×107s-1 (λmax=360nm) and has a lifetime of ~1.4µs. T1K of 6 decays to form ketyl radical 7 (λmax ~300nm), which dimerizes to form photoproducts, pinacol derivatives 8 and 9. In comparison, photolysis of trans-phenyl(2-phenylcyclopropyl)methanone 1 in argon-saturated chloroform-d results in cis-phenyl(2-phenylcyclopropyl)methanone 2 and a smaller amount of 3, presumably through 1,3-biradical 11. Nanosecond laser flash photolysis of 1 does not reveal significant transient absorption, although the T1K of 1 is detected with phosphorescence at 77K. Density functional theory calculations were used to elucidate the triplet reactivity of 1, 2 and 6 by comparing the feasibility of H atom abstraction, cyclopropyl cleavage and [beta]-quenching of their triplet ketones. Copyright © 2014 John Wiley & Sons, Ltd.